SOME EFFECTS OF HURRICANE AGNES ON WATER QUALITY I N THE PATUXENT RIVER ESTUARY

David A. Flemer R. E. Ulanowicz

Chesapeake B i o l o g i c a l Labora tory U n i v e r s i t y of Maryland

Solomons, Maryland and

Donald L. Tay lo r , Jr. Department of Biology

Col lege of Will iam and Mary Will iamsburg, V i r g i n i a

A b s t r a c t

A post-Agnes s tudy t h a t emphasized environmental f a c t o r s was c a r r i e d o u t on t h e Pa tuxen t R ive r e s t u a r y wi th weekly sampling a t e i g h t s t a t i o n s from 28 June t o 30 August 1972. S p a t i a l and temporal changes i n t h e d i s t r i b u t i o n o f many f a c t o r s , e .g . , s a l i n i t y , d i s s o l v e d oxygen, s e s t o n , p a r t i c u l a t e carbon and n i t r o g e n , i n o r g a n i c and o r g a n i c f r a c t i o n s of d i s s o l v e d n i t r o g e n and phosphorus, and c h l o r o p h y l l 5 w e r e s t u d i e d and compared t o e x t e n s i v e e a r l i e r r eco rds . P a t t e r n s shown by t h e p r e s e n t d a t a were compared e s p e c i a l l y wi th a l o c a l heavy s torm t h a t occur red i n t h e Pa tuxen t d r a i n a g e b a s i n du r ing J u l y 1969. Es t ima tes were made of t h e amounts of m a t e r i a l c o n t r i b u t e d v i a upland d ra inage . A f i r s t approximation i n d i c a t e d t h a t 14.8 x l o 3 m e t r i c t o n s of s e s t o n were c o n t r i b u t e d t o t h e head of t h e e s t u a r y between 21 and 24 June. We e s t i m a t e d t h a t 5.6 x 103 m e t r i c tons o f s e s t o n w e r e d e l i v e r e d t o t h e upper e s t u a r y between 28 June and 30 August. P a r t i c u l a t e carbon was 5% o f t h e s e s t o n dur ing t h e l a t t e r pe r iod . The p a r t i c u l a t e carbon:ni t rogen r a t i o ( w t / w t ) of t h e m a t e r i a l c o n t r i b u t e d f o r t h e 10-week i n t e r v a l , e x c l u s i v e of t h e four-day peak f low, was about 4.7: l . From 28 June t o 30 August we e s t ima ted t h a t about 135 m e t r i c t o n s o f t o t a l d i s s o l v e d n i t r o g e n and 10.8 m e t r i c t o n s o f t o t a l d i s s o l v e d phosphorus were added t o t h e e s t u a r y . These amounts of n i t r o g e n and phosphorus g r e a t l y exceeded t h e requi rement f o r p l a n t primary p roduc t ion , e s p e c i a l l y d u r i n g J u l y . Some i n t e r e s t i n g c o r r e l a t i o n s were observed i n t h e d a t a . P a r t i c u l a t e n i t r o g e n and a c t i v e c h l o r o p h y l l 5 were u s u a l l y c o r r e l a t e d w i t h a c o r r e l a t i o n c o e f f i c i e n t of 1 0.80 (9 d . f . ) i n t h e lower s t u d y a r e a . I n t h e t i d a l f r e s h w a t e r a r e a (Nottingham) , NH3-N and NO -N and t o t a l d i s s o l v e d phosphorus were nega&vely c o r r e l a t e d w i t h ch?orphy l l 5. These c o r r e l a t i o n s were n o t s t r o n g i n t h e lower r i v e r . The atomic r a t i o of d i s s o l v e d i n o r g a n i c n i t r o g e n t o d i s s o l v e d i n o r g a n i c phos- phate-phosphorus was u s u a l l y g r e a t e r t han 1 5 and o f t e n above 30, e s p e c i a l l y a t t h e most seaward s t a t i o n (nea r Solomons) and i n t h e t i d a l f r e shwa te r s . During August some of t h e above r a t i o s were less than 2.0 i n t h e middle p o r t i o n o f t h e e s t u a r y ; t h i s sugges ted t h a t n i t r o g e n would p o t e n t i a l l y become more l i m i t i n g t o phytoplankton growth than phosphorus. A t t h i s t i m e t h e c o n c e n t r a t i o n of a c t i v e ch lo rophy l l 5 o f t e n approximated 30 t o 60 mg m-3. The minimum s u r f a c e s a l i n i t y a t Sandy P o i n t , t h e most seaward s t a t i o n n e a r Solomons, was 1900 and occur red on 5 J u l y . S t rong v e r t i c a l d i f f e r e n c e s i n s a l i n i t y were noted i n t h e middle p o r t i o n of t h e r i v e r . I n t h i s r e g i o n , bottom d i s s o l v e d oxygen v a l u e s were f r e q u e n t l y <1.0 mg liter-1.

Introduction

Aside from the obvious destruction that large cyclonic storms in-

cur, there is an opportunity to learn much about the response of coastal

estuarine ecosystems from such perturbations. Hurricane Agnes entered

the ,Chesapeake Bay area on 21 June 1972 and provided a unique opportunity

to study the environmental impact of an event which usually is unavailable

to estuarine scientists. Logistically? we were conveniently located on

the Patuxent River estuary to engage in a field reconnaissance of several

environmental factors, e.g., salinity, dissolved oxygen, nutrients, chloro-

phyll5,and seston. It was fortunate to have recently completed a field

analysis of the above and other factors in the upper estuary between

August 1968 and August 1970 (Flemer et al., 1970, much of this information

will be published later). Thus our present efforts have considerable

comparative value.

Though not as unique or as formidable as Hurricane Agnes, an unusually

heavy rainfall in the Patuxent drainage area occurred during late July

1969, and we compared the 1969 data with the present data. Our field

studies in this investigation began on 28 June 1972, about one week after

Agnes unleashed her fury in the Patuxent, and they were continued at

weekly intervals until 30 August 1972. This report provides a summary and

interpretations of the environmental data.

Extreme conditions imposed by Agnes were believed of general interest

in the area of eutrophication. This study was planned to help character-

ize the relationship between phytoplankton and nitrogen and phosphorus.

Questions regarding nutrient removal at wastewater treatment plants is

still an unresolved problem in Maryland, and an active research program

in Chesapeake Bay is focusing on the effects of sewage on the estuarine

ecosystem (Chesapeake Research Consortium, Inc., proposal under develop-

ment) . Detritus is considered an important source of energy for many de-

posit- and filter-feeding organisms. In the oligohaline area of the

Pa tuxen t , w e have provided f u r t h e r evidence t h a t t h e dominant s p r i n g

copepod, Eurytemora a f f i n i s , f e e d s e x t e n s i v e l y on d e t r i t u s (Heinle e t a l . ,

1974). W e have a t t empted t o c h a r a c t e r i z e t h e i n p u t of d e t r i t u s t o t h e

head of t h e e s t u a r y fo l lowing t h e l a r g e runof f caused by Agnes. The

e lementa l composit ion of t h e suspended m a t e r i a l i n t h e e s t u a r y complements

work r e p o r t e d i n a r e c e n t symposium (Melch io r r i -San to l in i and Hopton,

19721, though r e l a t i v e l y l i t t l e in fo rma t ion was p resen ted f o r e s t u a r i n e

cond i t ions . Des,c,r ipt ion of bhe Study Area

The d r a i n a g e b a s i n o f about 963 sq . m i l e s (2,494 km2) l i e s wholly

wi th in t h e S t a t e of Maryland on t h e wes te rn shore o f t h e Bay and forms

t h e n e x t major t r i b u t a r y upstream from t h e Potomac Rive r (Nash, 1947) .

The b a s i n l i e s i n bo th t h e Piedmont P l a t e a u and t h e C o a s t a l P l a i n physio-

g raph ic p rov inces . Urban iza t ion i s o c c u r r i n g , e s p e c i a l l y i n t h e upper

dra inage b a s i n n e a r t h e F a l l Line , which r u n s approximately between

Washington, D. C. and Bal t imore . Ex tens ive t i d a l b r a c k i s h wa te r marshes

a r e l o c a t e d w i t h i n t h e upper two- th i rds of t h e s tudy a r e a w i t h t h e sea-

ward e x t e n s i o n of t h e marsh complex ending j u s t upstream t o Trueman P t .

(Fig. 1) . The p r e s e n t s t u d y a r e a inc luded e i g h t channel s t a t i o n s from t i d a l

f r e shwa te r (Nottingham) t o a l o c a t i o n a d j a c e n t t o Solomons (Sandy P t . ) . T i d a l ampl i tude i s smal l . Cory and Nauman (1967) r e p o r t a d i f f e r e n c e

of 0.55 m between mean h igh and mean low t i d e s n e a r Benedic t Br. and

Mansueti (1961) gave a t i d a l range 0 f ~ 0 . 7 6 m n e a r Nottingham. The e s t u a r y

is t y p i c a l l y a two-layered system ( t y p e B of P r i t c h a r d , 1955) and o c c a s i o n a l l y

changes t o a th ree - l aye red system n e a r t h e mouth.

Methods and Procedures

F ie ld Sampling Procedures

F i e l d samples w e r e ob t i aned w i t h a 1 3 - f t . Boston Whaler. Sampling

began a t Sandy P t . and proceded upstream fo l lowing t h e node of t h e same

s lack c u r r e n t t h a t preceded f l o o d c u r r e n t . Water samples w e r e pumped w i t h

Dissolved oxygen and temperature were measured wi th a YSI Model 5 4 oxygen

meter by p lac ing t h e probe near t h e end of t h e sampling hose i n a p l a s t i c

bucket. S a l i n i t y was measured wi th an American o p t i c a l Co. r e f rac tomete r

, p r i o r t o 19 J u l y , and a Beckman Model RS-5 sa l inometer was used a f t e r t h i s

da te . Samples were brought back t o t h e l abora to ry and processed. F i l t r a t e s

and u n f i l t e r e d samples were f rozen i n g o l y e t h y l e n e b o t t l e s . F i l t e r pads

were des icca ted over s i l i c a g e l and f rozen. Chlorophyll a samples col-

l e c t e d on f i l t e r s were d i r e c t l y f rozen wi thout d e s i c c a t i o n .

Ana ly t i ca l Methods

Samples f o r ch lo rophyl l 5 were c o l l e c t e d on Whatman GF/C f i l t e r s and

t h e ch lo rophyl l 2 was es t imated f l u o r o m e t r i c a l l y wi th a Turner f luorometer

(Yentsch and Menzel, 1963; Holm-Hansen e t a l . , 1965). Our adap ta t ion of

t h e s e two methods is desc r ibed i n d e t a i l (Flemer e t a l . , 1970).

Ses ton, o r t o t a l suspended m a t e r i a l , was determined on t a r e d GF/C

f i l t e r s a f t e r drying t o cons tan t weight over s i l i c a g e l .

Pa r tLcu la te carbon was determined by t h e method of Menzel and Vaccaro

(1964) us ing a Beckman Model 1R215 I n f r a r e d Analyzer and a Coleman CHO

Analyzer. P a r t i c u l a t e n i t rogen was determined wi th a Coleman Model 29A

Nitrogen Analyzer equipped wi th a Model 29 combustion tube and syr inge.

T o t a l phosphorus was determined wi th t h e ox ida t ion method of Menzel

and Corwin (1965). The same method was used t o ox id ize d i s so lved

o rgan ic phosphorus m a t e r i a l s a f t e r pass ing t h e sample through a GF/C f i l t e r .

Dissolved inorgan ic r e a c t i v e phosphorus was determined w i t h t h e composite

reagen t method (S t r i ck land and Parsons, 1968).

Ammonia n i t rogen a n a l y s i s followed t h e procedure of Solorzano (1969).

N i t r a t e and n i t r i t e n i t rogen were analyzed by t h e method of

S t r i c k l a n d and Parsons (1965). Soluble o rgan ic n i t rogen a n a l y s i s employs l

a modif icat ion of t h e uv l i g h t ox ida t ion (S t r i ck land and Parsons, 1968). I

~ A h a l f - s t r e n g t h seawater s o l u t i o n i s used f o r t h e so lven t , f o r t h e blanks ,

ammonium s u l f a t e , and p y r i d i n e s t andards . The seawater s o l u t i o n is made

up according to Strickland's and Parsons' (1968) nitrate method, then

diluted by one-half with double distilled, deionized water. This

solution is to dilute river water samples and to add salts to facilitate

the uv oxidation (unpublished observations). We dilute, if necessary,

20 ml of river water sample to 100 ml with half-strength seawater. Two

drops of 30% hydrogen peroxide are added to the sample in a quartz tube,

and the sample is capped and irradiated 7 cm from a 1,200-watt Hanovia-

Englehardt 189A lamp for 3 hrs. Strickland's and Parsons' (1968) procedure

is followed for the remainder of the analysis.

Freshwater Discharge to the Head of the Estuary

Discharge values were calculated for the contribution of freshwater

from the drainage basin of the upper Patuxent River above the confluence

with Western Branch and for the Western Branch drainage basin. Gaging

stations were near the headwaters of the tributaries; thus, the estimates

of discharge were based on the ratio of area gaged to the area downstream

of the gaging stations. The formulation employed was based on the work of

Charles Hall, Maryland Department of Water Resources, where:

QT = QL + 5.9 Qw + 1.42 Qu + 4.2 QG

and

Qt = total freshwater to head of estuary (main stem of Patuxent, plus Western Branch)

QL = discharge at Laurel gaging station

= discharge at Western Branch gaging station near Largo

QU = discharge near Unity gaging station

QG = discharge near Guil'ford gaging station

The unpublished gaging station data were provided by the Geological

Survey, Water Resources Division, U. S. Department of Interior, College

Park, Maryland.

We determined the total discharge over at where the sampling date

was near the mid-point. For example, the first sampling date of 28 June

with three days before and three days after this date were used to esti-

mate the weekly discharge. The same approach was employed for each

C5

succeeding sampling d a t e . The c o n c e n t r a t i o n of a f a c t o r a t Nottingham, e.g.,

s e s t o n , was m u l t i p l i e d by t h e t o t a l weekly d i s c h a r g e t o e s t i m a t e a f l u x

f o r t h e i n t e r v a l . The 10 i n t e r v a l s were summed t o p rov ide an e s t i m a t e of

A l l d a t a t a k e n i n t h i s s tudy a r e l i s t e d i n Table 1 and appendix. l4

Water t empera tu res measured i n t h i s s tudy were c h a r a c t e r i s t i c f o r

t h e summer (Table 1; Flemer e t a l . , 1970) . Maximum v a l u e s o c c u r r e d u p -

s t r eam i n t h e g e n e r a l v i c i n i t y of t h e Chalk P o i n t Power P l a n t . Exceptionally

h igh v a l u e s , some approximating 360C, w e r e noted i n t h e upper s t u d y a r e a

on 26 J u l y . Bottom v a l u e s w e r e sometimes s l i g h t l y h i g h e r t h a n s u r f a c e

va lues . These d a t a supplement t h e e x t e n s i v e r e c o r d s of t empera tu re i n

t h e upper F i v e r (Herman e t a l . , 1968, and Cory and Nauman, 1967) .

S a l i n i t i e s r e f l e c t e d t h e l a r g e r a i n f a l l i n t h e d r a i n a g e b a s i n , and

o u r d a t a r e c o r d t h e r ecovery of t h e low s a l i n i t i e s back t o t h e more nor-

mal regime (Table 1). Sur face s a l i n i t i e s were 0.0 o/oo a s f a r seaward a s

Benedic t B r . d u r i n g most of J u l y . S t rong v e r t i c a l d i f f e r e n c e s i n s a l i n i t y

were noted a t Sher idan P t . and seaward. The minimum s u r f a c e s a l i n i t y a t

Sandy P t . was about 1 .0 o/oo and occur red on 5 J u l y . Bottom s a l i n i t i e s

on two occas ions a t Sandy P t . (28 June and 2 August) were abou t 1.5 o/oo

I I less t h a n s u r f a c e va lues . We p o i n t o u t t h e s e d i f f e r e n c e s a s p o s s i b l y

a c c u r a t e o b s e r v a t i o n s s i n c e Nash (1947) made s i m i l a r k inds of obse rva t ions

n e a r Sandy P t .

Some p e r s p e c t i v e i s ga ined by comparing s u r f a c e s a l i n i t i e s a t Sandy

P o i n t w i th t h o s e t aken nearby a t t h e Chesapeake B i o l o g i c a l Labora tory

p i e r . D a i l y s a l i n i t i e s a t t h e p i e r from 1 June t o 20 June 1972 ranged

between 7.9 and 10.8 o/oo. These d a t a a r e n o t cont inuous a s obse rva t ions

are u s u a l l y n o t made on weekends; however, on 28 June t h e s a l i n i t y was

2.5 o/oo and agreed c l o s e l y wi th o u r d a t a a t Sandy P o i n t . The monthly

mean v a l u e s a t t h e p i e r d u r i n g t h e pe r iod 1938 t o 1957 f o r June , J u l y ,

and August were 11 .0 , 12.5, and 13.5 o/oo, r e s p e c t i v e l y (Beaven, 1960) .

Hurricane Agnes r e s u l t e d i n very low s a l i n i t i e s a t a t ime when s a l i n i t i e s

normally proceed toward maximum v a l u e s i n t h e River .

S a l i n i t y d a t a o b t a i n e d dur ing J u l y 1969 r e f l e c t t h e a f t e r m a t h of a

heavy r a i n f a l l t h a t occur red i n t h e d r a i n a g e b a s i n . I n t h e lower R ive r ,

11.85 inches of r a i n f e l l a t Solomons on 23 J u l y 1969, ove r a p e r i o d of

a few hours (NOAA, Ashland, N. C . , c e n t r a l r e c o r d s f o r S O ~ O ~ O ~ S a r e a ) .

I n t h e upper River , t h e s u r f a c e s a l i n i t y a t Nottingham on 8 J u l y 1969 was

2.7 o/oo and on 30 J u l y 1969, t h i s s a l i n i t y l e v e l was d i s p l a c e d seaward

t o a p o i n t n e a r Trueman P t . (Flemer e t a l . , 1970) .

Informat ion i s p resen ted on d i s s o l v e d oxygen t h a t g e n e r a l l y c h a r a c t e r -

i z e s t h e oxygen r e s o u r c e s o f t h e River (Table 1). Only l a r g e changes can

be e v a l u a t e d f o r t h e summer s i n c e t h e same s l a c k sampling r e q u i r e d some

c r u i s e s t o be i n i t i a t e d a t n i g h t . Very low c o n c e n t r a t i o n s of d i s s o l v e d

oxygen I e .g. I 1.0 mg liter'l, were measured i n bottom wa te r s between

Sheridan P t . and Broome Is.

P a r t i c u l a t e M a t e r i a l

Ses ton . Highes t c o n c e n t r a t i o n s of s e s t o n occur red upstream of ene edict B r .

(Fig. 2 ) . A maximum v a l u e of 170 mg li ter-1 was measured a t Lower Marlboro

i n t h e bottom sample on 5 J u l y . Seaward t o Benedic t Br. t h e c o n c e n t r a t i o n

of s e s t o n seldom was g r e a t e r t h a n 50 mg liter'l. On 2 August, 168 mg

li ter-l of s e s t o n w e r e recorded a t Nottingham, and 68 mg liter'l of

se s ton w e r e measured a s f a r seaward a sBroome Is. The above p a t t e r n of

se s ton i n t h e River s u g g e s t s t h a t t h e maximum d i scha rge of suspended s o l i d s

a s s o c i a t e d w i t h Agnes occur red b e f o r e 28 June . The r a p i d washout of

ch lo rophy l l - a , a s d i s c u s s e d l a t e r , confirms t h i s conclus ion .

High s e s t o n i c l e v e l s w e r e o f t e n encountered dur ing e a r l i e r work i n

t h e River (Flemer e t a l . , 1970) . The upper t i d a l Pa tuxen t r e c e i v e d very

high amounts of s e s t o n dur ing l a t e J u l y 1969. S e v e r a l v a l u e s approached

200 mg l i t e r - l . We have no q u a n t i t a t i v e d a t a on s e s t o n f o r t h i s e v e n t a t

Solomons, b u t comparat ive d a t a f o r t h e upper t i d a l River t aken on 8 J u l y

and 30 J u l y 1969 documented t h e impact o f t h i s unusua l ly l a r g e f r e s h -

wa te r d i s c h a r g e t o t h e e s t u a r y . These d a t a i n d i c a t e d t h a t t h e Pa tuxen t

River has r e c e i v e d l a r g e c o n c e n t r a t i o n s of s e s t o n i n t h e p a s t b u t Hurr icane

Agnes was a s i g n i f i c a n t e v e n t i n t h e h i s t o r y of t h e Pa tuxen t system.

Normally t h e so -ca l l ed "sediment t r a p , " which is w e l l d e s c r i b e d f o r t h e

main s t e m of Chesapeake Bay (Schubel , 1968b; Schubel and Biggs, 19691,

ex tends seaward i n t h e Pa tuxen t e s t u a r y t o about Chalk P t . Hurr icane

Agnes b r i e f l y extended t h e seaward boundary of t h e sediment t r a p down-

stream t o , a t l e a s t , t h e mouth of t h e Pa tuxen t River . The system r e t u r n e d

q u i c k l y t o s t e a d y - s t a t e c o n d i t i o n s , and t h e seaward e x t e n s i o n of t h e

sediment t r a p moved upstream between Benedic t Br. and Sher idan P t .

Chlorophyl l 5. The c o n c e n t r a t i o n of a c t i v e c h l o r o p h y l l 2, which i s an in-

dex of t h e s t a n d i n g c rop of phytoplankton ( h e r e p o s s i b l y some mud-dwelling algae)

showed a s h a r p d e c l i n e between Nottingham and Sher idan P t . (F igs . 3a and

3b) d u r i n g t h e f i r s t two sampling p e r i o d s . Sur face v a l u e s a t t h i s t i m e

w e r e 5 t o 8 mg m-3. Seaward, between Broome Is. and Sandy P t . , t h e s u r - f a c e c o n c e n t r a t i o n of c h l o r o p h y l l 5 ranged between 40 t o 50 mg mW3. T h i s

p a t t e r n probably r e s u l t e d from t h e seaward d isp lacement of normally higli

upstream c o n c e n t r a t i o n s . E a r l i e r work i n d i c a t e d t h a t t h e h igh v a l u e s

observed dur ing t h i s s tudy between Nottingham and Trueman P t ; from 19

J u l y t o 30 August a r e t y p i c a l f o r t h e upper s tudy ' a r e a (Flemer e t a l . ,

1970) . Maximum s u r f a c e c o n c e n t r a t i o n s of c h l o r o p h y l l & .obse rved dur ing

t h e p r e s e n t s t u d y were 127 and 105 mg m-3, which occurred a t Nottingham

and Broome Is. on 9 August and 23 August, r e s p e c t i v e l y . Most modera te ly

deep tempera te E a s t Coas t e s t u a r i e s show a s i n g l e s u s t a i n e d maximum con-

c e n t r a t i o n of c h l o r o p h y l l 2 d u r i n g t h e l a t e summer, e s p e c i a l l y i n t h e

sediment t r a p a r e a (Ryther , 1963; Flemer, 1970) .

Seaward of Lower Marlboro t h e r e was a s t r o n g e r tempora l p a t t e r n i n

t h e d i s t r i b u t i o n of s u r f a c e c h l o r o p h y l l 5 i n t h e p r e s e n t s tudy than t h a t

observed f o r t h e bottom wa te r s . The low va lues measured a t Queen Tree

C 8

and Broome Is. were assoc ia ted with the low concentra t ion of d i s so lved

oxygen t h a t was p resen t i n t he bottom waters. I n genera l , the concentra-

t i on of chlorophyl l a observed i n the p resen t s tudy compares w e l l wi th

e a r l i e r s t u d i e s on the River (Flemer and Olmon, 1971; Flemer e t a l . , 1970).

A f e a tu r e c h a r a c t e r i s t i c of Hurricane Agnes was f o r more v a r i a t i o n s over

time t o occur i n the sur face waters a t h igher s a l i n i t i e s .

For perspec t ive , we a r e ab le t o compare the p r e sen t d i s t r i b u t i o n of

chlorophyl l 5 i n t he r i v e r wi th t h a t f o r t he summer of 1969. The l a rge

amount of r a i n t h a t occurred i n l a t e Ju ly 1969 was s t r ong ly assoc ia ted

with t he low ch lorophyl l 5 values measured a t t h a t time. For example,

values a t Lower Marlboro rap id ly decreased from 46 t o 7 mg m-3. This

c o r r e l a t e s wel l with t he increased s e s t o n i c load received by t he River

during t h e Ju ly 1969 per iod and i l l u s t r a t e s t h a t t he upper Patuxent has

experienced an important washout of t h e phytoplankton a t o the r times.

P a r t i c u l a t e carbo'h. The concentra t ion of p a r t i c u l a t e carbon showed a s u r -

p r i s i n g u n i f o r m i t y i n t he sur facewate rs through most of t he River u n t i l e a r l y

August (Fig. 4a) . Most values ranged between 100 and 200 u moles l i t e r - '

(1-2 - 2.4 mg l i t e r - l ) . Highest concentra t ions of p a r t i c u l a t e carbon i n

the su r f ace and bottom waters (Fig. 4b )occu r r eddu r ing l a t e August when

chlorophy 11 5 values were maximal.

We observed t h a t t he average values of t h e percen t of carbon r e l a t i v e

t o ses ton i n the su r f ace waters ranged between 6 and 8% from ~ o t t i n g h a m

seaward t o Queen Tree (Table 2 ) . Exclusive of two unusually high concen-

t r a t i o n s of p a r t i c u l a t e carbon n o t e k a t Broome Is. and Sandy P t . , t h e

values averaged 8.6 and 10.7% a t t he se s t a t i o n s . The average values d i s -

cussed above compare favorably t o e a r l i e r work on the River (Flemer e t a l . ,

1970).

Seaward of B e n e d i c t ~ r . the percen t of carbon r e l a t i v e t o ses ton i n

bottom samples was about one-half l e s s than t he su r f ace average values.

Several reasons may he lp exp la in these observat ions . Possibly a d i f f e r en -

t i a l s e t t l i n g of inorganic ma t e r i a l occurred, o r t he r o l e of decomposition

drainage, and p l a n t product ion i n t h e River. Also, d i l u t i o n of t h e bottom

suspended m a t e r i a l from t h e sediments could in f luence t h e above p a t t e r n

(Schubel and Biggs, 1969). I f w e assume t h a t t h e carbon va lues r e p r e s e n t

about 50% of t h e o rgan ic mat te r on a d ry weight b a s i s , then our va lues

agree more c l o s e l y wi th t h e win te r and spr ing d a t a on o rgan ic mat te r i n

t h e upper Chesapeake Bay (Schubel, m68a) .

P a r t i c u l a t e n i t rogen . I n c o n t r a s t t o t h e d i s t r i b u t i o n o f p a r t i c u l a t e c a r b o n ,

p a r t i c u l a t e n i t rogen i n t h e su r face waters v a r i e d more wi th time than it did

p o s i t i o n i n t h e r i v e r . Most maximum va lues approximated 40 t o 50 u moles

l i ter ' ' o r 600 t o 750 ug l i ter ' ' (Fig. 5 a ) . The f a i r l y high c o r r e l a t i o n

between n i t rogen and ch lo rophyl l a i s obvious from t h e contour diagrams.

Conversely, t h e p a t t e r n of p a r t i c u l a t e n i t r o g e n i n t h e bottom waters was

c h a r a c t e r i z e d more by p o s i t i o n than time i n t h e r i v e r ; i n f a c t , a r e l a t i v e l y

sharp decrease occurred throughout t h e s tudy i n t h e concen t ra t ion of p a r t i -

c u l a t e n i t rogen a t Sheridan P t . (Fig. 5b) . A s i m i l a r t r e n d was noted f o r

ch lo rophyl l a. The concen t ra t ion of p a r t i c u l a t e n i t r o g e n measured dur ing

t h i s s tudy approximated t h a t measured p rev ious ly (Flemer e t a l . , 1970).

N u t r i e n t s

Phosphorus. Data on s e v e r a l f r a c t i o n s of phosphorus, e.g., t o t a l phosphorus,

t o t a l d i s so lved phosphorus, and d i s so lved inorgan ic r e a c t i v e phosphate-phosphorus

a r e i l l u s t r a t e d i n Fig . 6 f o r f o u r s t a t i o n s along t h e River. To ta l phos-

phorus approximated 6.0 ug a t liter'' a t Nottingham and showed a gradual

decrease seaward t o Sandy P t . where t h e concen t ra t ion ranged between 2 and

4 vg a t l i t e r ' l , Inadver ten t f i l t r p t i o n of samples from 5 J u l y through 19

J u l y prevented a n a l y s i s f o r t o t a l phosphorus. T o t a l d i s so lved phosphorus

u s u a l l y ranged between 20 and 50% of t h e t o t a l phosphorus. Thus, by d i f -

f e rence , p a r t i c u l a t e phosphorus c o n s t i t u t e d a s u b s t a n t i a l p o r t i o n of t h e

phosphorus i n t h e r i v e r . Dissolved inorgan ic phosphate usua l ly accounted

f o r most of t h e t o t a l dissolved phosphorus. Therefore, r e l a t i v e l y l i t t l e

dissolved organic phosphorus was present . On a few occasions t he dissolved

inorganic values were ana ly t i ca l l y g r e a t e r than values f o r t o t a l dissolved

phosphorus. W e bel ieve t h a t t he t o t a l dissolved values should be considered

only approximate. Work is under way i n an attempt t o reso lve t h i s problem.

Compared t o da ta obtained durigg t h e summer of 1969, w e conclude

t h a t t he general pa t t e rn of phosphorus d i s t r i b u t i o n and concentrat ions i n

the River d id no t d i f f e r i n any important way (see Fig.6).

W e should mention t h a t t he inorganic phosphate concentrat ion i s l a rge ly

control led i n t u rb id e s t u a r i e s through sorp t ion r eac t ions with suspended

sediments (Pomeroy, Smith, and Grant, 1965). We expect t h a t such r eac t ions

strongly influenced the l e v e l of phosphate observed i n the presen t study

as the Patuxent q u a l i f i e s a s a tu rb id estuary. The exchange is apparently

near-equilibrium when the water has a phosphorus content about 0.7 t o 1.5 i.~g

a t l i t e r 1 ( ~ u t l e r and T i b b i t t s , 1972). I n t he Tamar es tuary , near t he

Plymouth Laboratory, England, i n con t r a s t t o our f indings, the t o t a l dissolved

phosphorus was r e l a t i v e l y constant before and a f t e r a heavy r a i n throughout

the estuary. The concentration of t o t a l dissolved phosphorus i n t he Patuxent

showed a s u b s t a n t i a l decrease from Nottingham seaward but r e l a t i v e l y l e s s

change over t i m e during the present study.

Nitrogen. W'itrogen determinations presented i n Fig. 7 show the t o t a l n i t ro -

gen as represented by severa l f r ac t i ons . The dissolved organic and inorganic

f rac t ions ( N H ~ , NO;, and NO;) a r e added t o t h e p a r t i c u l a t e nitrogen. Some

comparative da t a taken during the summer of 1969 a r e included on the

f igure (Flemer e t a l . , 1970) . Maximum t o t a l ni t rogen occurred a t Nottingham and during the f i r s t

s i x weeks many values ranged between 80 and 100 i.~g a t l i t e r - l . ~ o s t

values of t o t a l ni t rogen during the f i r s t s i x weeks a t Benedict B r . and

Queen Tree ranged between 60 and 80 pg a t liter''. ~t Sandy Pt . during

t h i s period the re was a s l i g h t increase i n the t o t a l nitrogen. A maximum

va lue f o r t h e e n t i r e s tudy of 146 pg a t l i t e r m 1 occurred a t Sandy P t . on

28 June which presumably was r e l a t e d t o t h e d i s p l a c e d upstream m a t e r i a l .

T o t a l n i t r o g e n decreased about 50% a t a l l s t a t i o n s dur ing the l a t t e r h a l f

of t h e s tudy w i t h few except ions . One no tab le excep t ion occurred a t Not-

tingham on 30 August where a concen t ra t ion of 140 vg a t l i t e r - ' was measured.

The l i m i t e d d a t a a v a i l a b l e from t h e summer of 1969 suggest t h a t t o t a l

n i t r o g e n was more h igh ly c o n c e n t r a t e c d u r i n g t h e recovery pe r iod of Agnes

t h a n noted dur ing t h e summer of 1969. By comparison, t h e concen t ra t ion of

t o t a l phosphorus f a i l e d t o show a c o n s i s t e n t i n c r e a s e over t h a t of t h e sum-

m e r of 1969.

We examined t h e r e l a t i v e p ropor t ion of NH3-N, N O ~ - N , and NO3-N t o t h e

t o t a l inorgan ic n i t r o g e n ( see Appendix). The concen t ra t ion of NH3-N de-

c reased more r a p i d l y than t h e c o n c e n t r a t i o n of N03-N a t Nottingham and

Benedict B r . from 28 June t o 19 Ju ly . The p a t t e r n was n o t a s c l e a r l y

d i s c e r n i b l e a tQueen Tree a s noted a t t h e upstream s t a t i o n s . A t Sandy P t .

t h e concen t ra t ions of NH3-N and NO3-N decreased t o g e t h e r p r o p o r t i o n a l l y

f o r most of t h e s tudy w i t h t h e pronounced excep t ion on 30 August. I t is

tempting t o a s c r i b e t h e more r a p i d dec rease i n NH3-N r e l a t i v e t o NO3-N

t o d i f f e r e n t i a l uptake by phytoplankton (Harvey, 1960). The a n a l y s i s i s

complicated by a r a p i d i n c r e a s e i n primary product ion, unknown changes i n

t h e r e l a t i v e r a t e of supply of t h e two n u t r i e n t s and n i t r i f i c a t i o n . N i t r i t e -

n i t r o g e n was q u a n t i t a t i v e l y unimportant compared t o t h e o t h e r inorgan ic

n i t r o g e n sources throughout t h e s tudy.

The concen t ra t ion of d i seo lved o rgan ic n i t r o g e n o f t e n approximated

o r exceeded t h e concen t ra t ion of d i s s o l v e d inorgan ic n i t r o g e n (Fig. 7 ) .

Most of t h e d i s so lved n i t r o g e n was i n t h e form of d i s s o l v e d o r g a n i c n i t r o -

gen a t Benedict B r . and Queen Tree on 9 , 16 , and 23 August (Appendix 1).

A t t h i s t i m e t h e s i g n i f i c a n c e of d i s s o l v e d o rgan ic n i t r o g e n t o t h e bio-

l o g i c a l system is n o t apparent b u t presumably c o n t r i b u t e s t o t h e a v a i l -

a b l e n i t rogen pool i n t h e long-term.

Ratios and Correlat ions

Data on C:N r a t i o s (atomic) f o r sur face and bottom waters a r e given

i n Figs. 8a and 8b. Surface r a t i o s showed more var ia t ion with time than

pos i t ion along the ax is of t he estuary. Both surface and bottom r a t i o s

usual ly were within the range of 3-10. Living phytoplankton typ i ca l l y

have a C:N (atomic) r a t i o of about 7 (Str ickland, 1960). The r e l a t i v e con-

stancy of t he r a t i o s i s d i s s imi l a r t o t he da ta reported f o r t he upper

Chesapeake Bay (Flemer and Biggs, 1971). However, maximum values i n t he

upper Chesapeake Bay usual ly followed the maximum discharge r e l a t e d t o

snow melt i n the Susquehanna River basin. Possibly the small range i n

values over the summer i n the Patuxent resu l ted from averaging the high

C:N r a t i o s associated with higher p l an t mater ia l with t he lower r a t i o s

associated with phytoplankton (Gucluer and Gross, 1964) . Par t i cu l a t e carbon (PC) was highly correlated,-,--p 0.80, with PN a t .-

Trueman Pt . (bottom) , Broome Is. (surface and bottom) , and Sandy P t .

(surface and bottom; Table 3 ) . A t Sheridan P t . and seaward, except

Queen Tree, we observed t h a t PC with chlorophyll and PN with chlorophyll

a were s i g n i f i c a n t l y eorse la ted (Table 3 ) . These co r r e l a t i ons a r e more - l i ke ly i n the more seaward region of t he estuary where phytoplanktonic

mater ia l i s r e l a t i v e l y more abundant than upstream where considerable

mater ia l i s derived from upland drainage. In e a r l i e r work we observed

t h a t P N x chlorophyll were highly cor re la ted a t the more seaward s t a -

t i ons , (e.g., Trueman Pt . and seaward t o Queen Tree) . Brooks (1970) re-

ported f o r the Brazos River, Texas, t h a t t he p a r t i c u l a t e organic carbon

was d i r e c t l y r e l a t ed t o r i v e r discharge. In the Patuxent autochthonous

sources of p a r t i c u l a t e organic carson probably mask the r e l a t i onsh ip be-

tween r i v e r flow and the concentration of p a r t i c u l a t e carbon, e spec i a l l y

a t t he more seaward s t a t i o n s .

The measured r a t i o of PC:chlorophyll i s another way t o view the

r e l a t i onsh ip between l i v ing a l g a l mater ia l and the t o t a l suspended par-

t i c u l a t e carbon (Figs. 9a and 9b). High r a t i o s i nd i ca t e a r e l a t i v e l y low

contr ibut ion of l i v ing p l an t mater ia l . Throughout most of t he study the

r a t i o was l e s s than 100:1, and f requen t ly values between 35 and 50:l were

observed. These r a t i o s a r e c o n s i s t e n t l y l e s s than those observed during

e a r l i e r summer work on t h e River (Flemer e t a l . , 1970) and these low

r a t i o s a r e be l i eved t o be a t y p i c a l of temperate c o a s t a l waters. A s d i s -

cussed i n t h e preceding paragraph, t h e s e r a t i o s suggest a h igh percentage

of l i v i n g a l g a l carbon r e l a t i v e t o t h e t o t a l measured p a r t i c u l a t e carbon.

Many labora to ry a l g a l c u l t u r e s under good growth cond i t ions wi l1 ,have C:chl

a r a t i o s between 30:l and 50: l ( P a r s o n s e t a l . , 1961). Rat ios g r e a t e r

than 150:l were a s s o c i a t e d wi th t h e e a r l y washout of t h e phytoplankton,

and high r a t i o s followed t h e sudden d e c l i n e from r e l a t i v e l y high concen-

t r a t i o n s of ch lo rophyl l a, e s p e c i a l l y a t Benedict B r . and seaward dur ing

t h e l a t t e r p a r t of t h i s study. We attempted t o use t h e r a t i o of 50:l of

PC:chlorophyll t o p a r t i t i o n t h e measured s u r f a c e PC i n t o t h a t r e l a t e d

t o l i v i n g phytoplankton and a r e s i d u a l (Fig. 1 0 ) . The r e s i d u a l would

presumably con ta in m a t e r i a l from such sources a s d e t r i t u s and smal l

he te ro t rophs . Some i n c o n s i s t e n t r e s u l t s were noted, e s p e c i a l l y a t t h e

most upstream s t a t i o n , Nottingham; however, t h e use of a reasonable b u t

s t i l l lower r a t i o of 30:l e l imina ted most i n c o n s i s t e n c i e s , except a t Not-

tingham. Average va lues by s t a t i o n , exc lus ive of Nottingham, of t h e per-

c e n t l i v i n g carbon ranged between 52 and 79%. No c l e a r a x i a l t r e n d along

t h e e s t u a r y was noted i n t h i s a n a l y s i s .

An e f f o r t was made t o a s s e s s t h e impact of Agnes i n terms of t h e

r a t i o d i s so lved inorganic n i t rogen ( D I N ) t o d i s so lved inorgan ic phosphate-

phosphorus ( D I P ) (Table 4 ) . Typ ica l ly , dur ing t h e summer i n many temperate

c o a s t a l wa te r s , t h e r a t i o s of D1N:DIP a r e l e s s than 15-10:l (Ryther and

Dunstan, 1971) which is i n t e r p r e t e d t h a t n i t rogen would probably become

l i m i t i n g t o phytoplanktonic growth before phosphorus. Frequent ly , t h e

r a t i o of D1N:DIP was less than 5: l dur ing t h e summer s t u d i e s of 1969 and

1970 (Flemer e t a l . , 1970). The r a t i o s i n t h e River following Agnes were

usua l ly very high, o f t e n between 15 and 50:1, except a t Benedict B r . and

Queen Tree from 9 August t o 23 August where s e v e r a l va lues approximated

1 t o 2. These low r a t i o s were genera l ly c o n s i s t e n t wi th high concentra t ions

ions

of ch lo rophy l l 2. The r a p i d d e c l i n e of t h i s bloom fol lowing t h e very

low D1N:DIP r a t i o is some evidence t h a t n i t r o g e n may have c o n t r o l l e d

maximum p l a n t biomass. A t Sandy P t . t h e r a t i o o f D1N:DIP remained f a i r l y

high, a f a c t which w e would n o t have p r e d i c t e d based on t h e p r e s e n t and

previous work i n t h e River. I t i s p o s s i b l e t h a t t h e n u t r i e n t regime i n

the main s t e m of t h e Bay in f luenced t h e p a t t e r n noted a t Sandy P t .

Many o t h e r c o r r e l a t i o n s a r e g iven i n Table 3. A t Nottingham many

of t h e n u t r i e n t f r a c t i o n s were c o r r e l a t e d , e .g . , NO3-N x t o t a l d i s s o l v e d

ni t rogen (TDN) , and TDN x DIP, and n u t r i e n t s were n e g a t i v e l y c o r r e l a t e d

wtih s e v e r a l p a r t i c u l a t e f r a c t i o n s , e .g . , NO3-N x ACL ( a c t i v e c h l o r o p h y l l

a ) . N u t r i e n t s would be expected t o dec rease a s p a r t i c u l a t e m a t e r i a l is - formed v i a pho tosyn thes i s . The l a c k of many of t h e s e h igh c o r r e l a t i o n s I

I

seaward t o Nottingham is evidence t h a t r e c y c l i n g probably dominated t h e I

n u t r i e n t uptake k i n e t i c s , e s p e c i a l l y from 9 t o 23 August.

The C:N:P r a t i o g i v e s some i n s i g h t i n t o t h e r e l a t i v e abundance of

elements i n t h e p a r t i c u l a t e m a t e r i a l . Though somewhat v a r i a b l e , l i v i n g

phytoplankton u s u a l l y a r e c h a r a c t e r i z e d by a C:N:P r a t i o of 106:lO-15:l

(Redfield e t a l . , 1963, and Ryther and Dunstan, 1971) . I n t h i s s tudy

N:P r a t i o s w e r e 1 0 : l t o 1 5 : l about h a l f o f t h e t i m e (Table 5 ) wi th t h e

remaining comparisons above o r below t h e r a t i o of 1 0 : l t o 1 5 : l . C t o

P was more v a r i a b l e than N t o P. I n 1 3 o u t of 25 comparisons, t h e C:P

r a t i o was less than 84:1, s i x t i m e s t h e r a t i o was between 85-126r1 and

s i x t i m e s t h e r a t i o was g r e a t e r than 127: l . These r a t i o s i n d i c a t e t h a t

o f t en t h e p a r t i c u l a t e m a t e r i a l i s r i c h e r i n P r e l a t i v e t o C. Below t h e

euphotic zone i n t h e ocean t h e p a r t i c u l a t e m a t e r i a l u s u a l l y i s phosphorus =. poor r e l a t i v e t o carbon and n i t r o g e n (Menzel and Ryther, 1964) . The

ques t ion i s s t i l l open rega rd ing t h e r e l a t i v e p ropor t ion of d i s s o l v e d

phosphorus t h a t i s a s s o c i a t e d w i t h i n o r g a n i c m a t e r i a l between t h e open

sea and c o a s t a l waters .

Flux of Mate r i a l t o t h e Head o f t h e Estuary

W e e s t ima ted t h a t about 5.6 x 103 m e t r i c t o n s of s e s t o n , 262 m e t r i c

tons of PC. 46 m e t r i c t o n s of PN, 135 m e t r i c t o n s o f TDN, and 11 m e t r i c

6 ) . During t h e peak f low from Agnes between 21 and 24 June , we e s t ima ted

t h a t 14.8 x 103 m e t r i c t o n s of s e s t o n were t r a n s p o r t e d t o t h e head of t h e

e s t u a r y . Th i s e s t i m a t e was based on an assumed c o n c e n t r a t i o n of 100 mg

l i t e r - ' s i n c e no d a t a on c o n c e n t r a t i o n s were a v a i l a b l e a t t h i s t ime. The

e s t i m a t e i s probably c o n s e r v a t i v e when compared t o o t h e r o b s e r v a t i o n s dur-

i n g h igh f lows (Flemer e t a l . , 1970)- F u r t h e r e s t i m a t e s a r e p o s s i b l e i f

we assume t h a t t h e r a t i o of t h e v a r i o u s f r a c t i o n s , e .g. , PC and TDN, re-

l a t i v e t o s e s t o n c o n t r i b u t e d between 2 5 June and 2 September would apply

dur ing peak f lows of Agnes. Th i s c rude approach y i e l d e d t h e fo l lowing

e s t i m a t e s of f l u x between 21 and 24 June: PC = 696, PN = 121, TDN = 352,

and TDP = 28 m e t r i c t o n s , r e s p e c t i v e l y .

I t is on ly p o s s i b l e t o g i v e a s e m i q u a n t i t a t i v e comparison of t h e

f l u x of m a t e r i a l between Agnes and J u l y 1969 s i n c e only t h r e e samples

were t aken between t h e end of June and t h e end of August 1969. However,

f o r s i m p l i c i t y , t h e r e l a t i v e f lows a r e i n s t r u c t i v e . We e s t i m a t e d t h a t

f o r 28 J u l y 1969 and 22 June 1972, t imes of peak f lows, t h a t 3,104 and

42,554 c f s of wa te r , r e s p e c t i v e l y , were d e l i v e r e d ko t h e head of t h e

e s t u a r y . A s a minimum, t h e impact of Agnes was 14 t imes t h a t of t h e r a in -

f a l l of J u l y 1969 i n terms of water t r a n s p o r t e d t o t h e upper e s t u a r i n e area .

I n t h e Pa tuxen t upland d r a i n a g e i s a s i g n i f i c a n t source of n u t r i e n t s .

I n t h e Ythan e s t u a r y , j u s t n o r t h of Aberdeen, Sco t l and , marine water con-

t r i b u t e d about 70% of t h e phosphate , and f r e s h w a t e r supp l i ed about 70% of

t h e n i t r a t e (Leach, 1971) . This a u t h o r p r e s e n t s i n t e r e s t i n g comparative

d a t a on t h e c o n t r i b u t i o n of n u t r i e n t s v i a f r e shwa te r . Based on a semi-

d i u r n a l t i d a l c y c l e (Like t h a t of t h e Chesapeake Bay) , t h e Ythan e s t u a r y

r e c e i v e d about 16.8 kg of i n o r g a n i c phosphate du r ing t h e summer. By

comparison, we e s t ima ted t h a t about 360 kg of t o t a l d i s s o l v e d phosphorus

p e r t i d a l c y c l e on t h e average e n t e r e d t h e Pa tuxen t e s t u a r y from upstream

between 25 June and 2 September. We should emphasize t h a t most of the

d i s s o l v e d phosphorus i n t h e Pa tuxen t i s a p p a r e n t l y i n o r g a n i c phosphate,

t h u s t h e comparison has v a l i d i t y .

Genera l D i scuss ion

E a r l i e r work i n t h e P a t u x e n t R ive r e s t u a r y showed t h a t t h e upper

t i d a l system p robab ly b o r d e r s on h y p e r t r o p h i c a t i o n ( S t r o s s and S t o t t l e -

myer, 1965; Herman e t a l . , 1968; and Flemer e t a l . , 1970) . Impor t an t

i nc reases i n r e c e n t y e a r s have o c c u r r e d i n pr imary p r o d u c t i v i t y , t h e

concen t r a t i on o f c h l o r o p h y l l 5, n i t r o g e n and phosphorus. The i n c r e a s e

i n a v a i l a b l e n i t r o g e n seems e s p e c i a l l y s t r i k i n g . I n view o f t h i s i n -

format ion , w e were e s p e c i a l l y i n t e r e s t e d i n t h e impact of ~ u r r i c a n e

Agnes a s a p o s s i b l e s t i m u l a n t t o f u r t h e r overenr ichment . I t i s s u r p r i s i n g

t h a t t h e P a t u x e n t i s s t i l l f r e e o f t h e mass ive b lueg reen a l g a l growths

so c h a r a c t e r i s t i c o f t h e upper Potomac e s t u a r y ( J aworsk i e t a l . , 1972) .

The d i l u t i o n s of t h e was t ewa te r s r e c e i v e d by t h e Pa tuxen t and Potomac

Rivers a r e q u i t e s i m i l a r (Brush, 1972) . Other f a c t o r s s u r e l y p l a y i m p o r t a n t

r o l e s . Fo r example, t h e e x t e n s i v e t i d a l marshes c h a r a c t e r i s t i c o f t h e

Pa tuxent , b u t n o t abundant i n t h e upper Potomac, may p l a y t h e r o l e of a

t e r t i a r y t r e a t m e n t system. S a l t marsh p l o t s n e a r Woods Hole, Mass.,

have been shown t o r e t a i n a l a r g e f r a c t i o n of t h e nitrogen and phosphorus

t h a t were e x p e r i m e n t a l l y added a s sewage s l u d g e ( V a l i e l a e t a l . , 1973) .

We a r e c u r r e n t l y s t u d y i n g t h e f l u x o f n u t r i e n t s between a marsh and i t s

dominant t i d a l c r e e k i n t h e upper Pa tuxen t ; however, r e s u l t s a r e unava i l -

a b l e f o r t h i s pape r (He in l e e t a l . , 1974) . P a r t i a l i n f o r m a t i o n i s a v a i l -

a b l e f o r t h e P a t u x e n t R ive r on t h e r a t e o f g r a z i n g a s an impor t an t c o n t r o l -

l i n g mechanism t o e x c e s s i v e a l g a l biomass (He in l e , i n p r e s s ) . I f an ad-

d i t i o n a l t r o p h i c l e v e l o c c u r s between phytoplankton and copepods, t h e n it

i s suspec t ed t h a t g r a z i n g w i l l be an i m p o r t a n t r e g u l a t o r t o t h e s t a n d i n g

c r o p of phytoplankton . Unfortunate&y, we were unab le t o o b t a i n d a t a on

zooplankton d u r i n g t h i s s t u d y t o a i d i n i n t e r p r e t a t i o n o f t h e i r r a t e o f

g raz ing d u r i n g t h e ex t reme hydrographic c o n d i t i o n s imposed by Hur r i cane

Agnes. I t must b e emphasized t h a t c o n d i t i o n s t h a t l e a d t o mass ive b lue -

green a l g a l growths a r e a problem i n e c o l o g i c a l s u c c e s s i o n and n o t s imply

one of up t ake k i n e t i c s o r development o f a l g a l biomass.

The f a c t t h a t modera te ly h i g h c o n c e n t r a t i o n s o f phy top lank ton ic b io-

mass o c n u r r e d d u r i n g t h i s s tudy compared t o p r e v i o u s s t u d i e s

i n t h e P a t u x e n t p robab ly i s s t r o n g l y l i n k e d t o washout. The

C17

apparent displacement of high chlorophyll levels typical of the sediment

trap area to the mouth of the River substantiates this conclusion of the

initial phase following Agnes. The sustained high levels of chlorophyll

a at the two upper stations after 26 July suggest that washout was of much - less significance at this time. The periods of low and high chlorophyll 5

concentrations seaward to lower Marlboro after about 26 July reflect the

dominance of other factors that are known to control phytoplankton biomass.

Though other nutrients were not measu?ed, we would suspect from the N:P

ratios that nitrogen played an important role. Welch et al. (1972) have

shown that phytoplankton blooms in the Duwamish estuary (Seattle, Wash-

ington) are strongly influenced by hydrographic conditions.

Comparative information obtained in our post-Agnes study shows that

factors measured in the Patuxent are high relative to most temperate estua-

ries; Thayer (1971) has summarized much of the pertinent data for these

systems. Little information is published on the effects of large floods

on water quality in temperate estuarine systems. A phenomenon of com-

parative interest are the monsoon rains that occur in some tropical areas.

These disturbances are a partial natural analog to Hurricane Agnes-in the

Patuxent. In the Cochin Backwater, S. W. India, the depth profile of nu-

trients, e.g. nitrogen and phosphorus, showed a marked seasonal change

induced by land runoff (Sankaranarayanan and Qasim, 1969). The system

changes annually from a marine estuary during the premonsoon period to a

freshwater system during the monsoon period. At times of maximum discharge

and turbidity, the quantity of settled detritus was comparatively low.

This resulted from the strong stratification or halocline that developed

in the estuary (Qasim and Sankaranarayanan, 1972). In S. E. India the

nutrients were increased with monsoon season in the Vellar estuary(Krish-

namurthy, 1967). For example, total phosphorus ranged between 1.01 and

5.05 pg at liter-' near the mouth of the Vellar estuary. We would not like

to overdraw the above comparison, but the partial environmental parallel

seemed worthy of mention.

Ratios of C:N:P and C:chl and N:chl 5 used to characterize the

particulate material suggest that some important effects resulted from

Georgia, British Columbia, the allochthonous organic material contributed

per year by upland drainage approximated the natural primary production

of the area (Seki, Stephens, and Parsons, 1969). Thus, for coastal bodies

of water, there is a broad range in the relative amount of PC derived from

land sources compared to natural primary production.

Acknowledgements

We thank Drew Brown and Bruce Lin??strom for their able field and lab-

oratory assistance. Shelley Sulkin and Linton Beaven helped with several

of the chemical analyses. Frances Younger provided the illustrations.

Partial financial support was provided by the U. S. Army Corps of Engineers

under Contract No. DACW31-73-C-0189.

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c21

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Table 1. Temperature (C), salinity (O/oo), and dissolved oxygen (mg liter -1), and top (T) and bottom (B), observed during the Patuxent River Post-Agnes Study, summer 1972.

S t a t i o n 6/28 7 /5 7/12 7/19 7/26 Temp. S a l . DO Temp. S a l . DO Temp. S a l . DO Temp. S a l . DO Temp. S a l . DO

Hours 1 4 : 1 5 08:15 1 3 : 3 5 07:05 1 3 : 4 5

N o t t i n g h a m T 24.7 0 .0 7.7 - 0.0 - 23 .6 0.0 6 .6 27.0 0 . 0 4 .8 29 .5 0 .0 7 .7 B 24.0 0 . 1 7 .2 - 0.0 - 23 .3 0.0 5 .7 26 .5 0 .0 4 . 7 34.5* 0 .0 6 . 5

L. Marlboro T 2 5 . 3 0 . 1 5 .2 - 0 . 0 - 23 .9 0 . 0 7 . 1 29 .0 0 .0 6 . 4 30.0 0 .0 9 . 8 B 25.0 0 . 1 5 . 3 - 0 . 0 - 23.5 0.0 6 . 6 30 .0 0 . 0 6 . 0 36.0* 0.0 6 .6

Trueman P t . T 27 .2 1 . 4 5 . 3 - 0.0 - 25.0 0 .0 7 . 0 29 .9 0 .0 7.0 30.0 0 .5 6 . 5 B 27.0 1 . 9 5 .6 - 0 .0 - 24.5 0 .0 6 .6 30 .0 0 .0 6 . 3 33 .3 1 .6 6 . 1

B e n e d i c t B r . T 26 .0 2 .5 5 . 3 24.0 0 .0 5 .4 25.4 0.0 7 . 2 28.0 0 .0 7 .2 29 .7 2 .3 6 . 7 B 25.8 2.6 5 .0 23.9 0 . 3 4 . 1 25 .2 1.1 6 . 5 27 .0 2 .4 6 . 5 32.0 2.6 6 .0

Q u e e n T r e e T 2 5 . 5 3.6 7 .0 23 .0 1 . 5 7 .8 2 4 . 5 2 .8 9 . 1 27.8 2 . 3 8 . 5 27.4 3.4 6.9 B 25 .0 4 . 4 2.6 21.2 4 .0 2 .5 23 .9 3 .4 3 . 5 23 .5 5 .0 1 . 5 26 .7 4.4 1 . 9

Sandy P t . T 26 .0 4.7* 6 .8 22 .0 1 . 3 8 .6 23 .9 4.5 9 . 1 25 .5 4 . 5 7.9 27 .0 5 .0 6 . 3 B 2 4 . 5 3 . 1 2 . 3 21.0 4 . 5 4 .2 22 .9 5 . 6 5 .4 24 .5 5 . 6 4 .6 27 .2 5 .0 4 . 3

H o u r s

Notes: a s t e r i s k mark u n u s u a l r e s u l t s . Time i n h o u r s o f i n i t i a t i o n o f s a m p l i n g i s g i v e n a t b o t t o m o f e a c h column a n d t i m e o f c o n c l u s i o n o f s a m p l i n g a t t h e u p s t r e a m s t a t i o n i s g i v e n a t t h e t o p o f e a c h co lumn.

T a b l e 1 C o n t i n u e d . T e m p e r a t u r e (C) , s a l i n i t y (O /oo ) , a n d d i s s o l v e d o x y g e n (mg liter-') , a n d t o p ( T ) a n d b o t t o m (B) I o b s e r v e d d u r l n g the P a t u x e n t R i v e r P o s t - A g n e s S t u d y , summer 1 9 7 2 .

S t a t i o n

H o u r s 07: 1 0 1 2 : 2 0 07:46 1 0 : 4 3 1 6 : 3 5

N o t t i n g h a m T 24.7 0 . 0 7 . 7 2 6 . 5 0 . 1 8 . 2 2 4 . 2 0 . 2 7 . 3 - - - 2 6 . 5 0 . 1 9 . 1 B 24 .0 0 . 1 7 . 2 25 .0 0 . 2 8 . 4 2 3 . 8 0 .2 7 . 1 - - - 2 6 . 5 0 . 1

L . M a r l b o r o T 2 5 . 3 0 .0 5 .2 27 .0 0 .0 6 . 8 2 5 . 0 0 . 8 6 . 4 - - - 2 7 . 5 0 . 3 B 2 5 . 0 0 . 1 5 . 3 26 .0 0 . 1 6 . 2 2 4 . 3 0 . 7 6 . 5 - - - 27 .5 0 . 3 7 .0

T r u e m a n P t . T 27 .2 1 .4 5 . 3 27 .5 0 . 9 7 . 8 2 5 . 1 2 . 2 6 . 7 27 .2 2 .8 6 .8 2 8 . 5 2 . 5 6 . 4 B 2 7 . 5 1 . 9 5 . 6 28 .0 1 . 0 6 . 8 2 4 . 5 2 . 4 6 .7 2 7 . 3 4 .0 7 . 0 2 9 . 5 3 . 1 6 .7

B e n e d i c t B r . T 26 .0 2 . 5 5 . 3 2 7 . 0 2 .7 7 . 8 2 4 . 1 5 . 4 5 . 5 27 .0 5 . 3 6 . 5 29 .0 5 . 7 B 25 .8 2 .6 5 .0 27 .0 2 .9 6 . 5 2 4 . 1 6 . 2 3 . 7 2 6 . 5 5 .6 5 . 3 28 .0 6 . 3

S h e r i d a n P t . T 2 5 . 5 3 . 1 5 . 3 2 6 . 5 3 .4 9 . 8 24 .5 5 .2 5 . 7 2 7 . 9 6 . 2 7 .9 25 .5 6 . 9 B 2 4 . 1 4 . 1 2 . 8 26.0 6 . 1 1.1 24 .0 7 . 6 0 . 3 2 5 . 3 7 . 3 1 . 6 26 .0 9 .7

Q ~ e e n T r e e T 2 5 . 5 3 . 6 7 . 0 26 .0 3 .8 9 . 4 24 .8 5 . 4 6 . 9 2 6 . 9 6 . 4 7 . 8 2 5 . 5 7 . 6 B 2 5 . 0 4 . 4 2 .6 25 .0 6 . 8 0 .9 2 4 . 0 7 . 9 0 .4 25 .0 8 . 0 0 . 9 2 6 . 5 1 0 . 4

B r o o m e I s . T 2 6 . 0 4 . 2 7 . 4 2 5 . 5 3 .9 1 0 . 3 24 .2 5 . 9 6 . 5 27.0 7 . 2 9 . 5 27 .0 7 . 8 5 . 2 B 2 4 . 5 4 . 7 2 . 7 2 0 . 3 9 . 3 0 . 4 24 .0 9 . 3 0 . 4 2 4 . 5 7 . 3 0 . 2 2 6 . 5 1 0 . 4 0 . 4

S a n d y P t . T 26 .0 4 . 7 * 6 . 8 2 5 . 1 6 . 0 8 . 6 2 4 . 0 7 .7 6 . 5 2 4 . 5 8 . 6 7 . 5 2 6 . 0 9 . 3 2 . 3 B 2 4 . 5 3 . 0 2 . 3 2 0 . 3 9 .8 1 . 4 24 .0 9 . 3 5 . 3 24 .5 9 . 5 3 . 8 2 4 . 5 1 0 . 4 2 . 6

Notes: * a s t e r i s k mark u n u s u a l r e s u l t s . Time i n h o u r s o f i n i t i a t i o n o f s a m p l i n g i s g i v e n a t b o t t o m o f e a c h co lumn a n d t i m e o f c o n c l u s i o n o f s a m p l i n g a t t h e u p s t r e a m s t a t i o n i s g i v e n a t t o p o f e a c h colprnn.

.,--- 1 , ) ,,A h n t t n m (RI w a t e r s . P o s t -

Table 2 . The percen t p a r t i c u l a t e carbon of s e s t o n i n t h e s u r f a c e ( S ) and bottom (B) waters , Post- Agnes Study, Patuxent River Es tuary , summer 1 9 7 2 .

STATIONS Nottingham Lower Marlboro Trueman P t . Benedict B r . Sheridan P t . Queen Tree Broome Is. Sandy P t .

6/28 4.8 4.0 - 3.3 2.6 2.8 2.6 2.2 2.7 2.3 4.5 1.4

2.1 3.8 3.8 4.3 1.4 5.0 8.1 4.0

7/13 5.0 4.0 4.4 4.0 3.5 4.2 2.7 2.9 4.3 2.1 2.9 5.0 7.5 2.9 11.5 2.5

7/19 0.9 3.1 5.0 5.0 4.2 5.0 4.7 7.6 3.9 2.8 7.9 2.8 7.9 3.6 12.0 11.2 I

I 7/26 4.8 5.6 4.4 3.0 3.0 5.1 4.0 6.0 3.6 5.6 2.8 5.0 4.5 3.6 9.0 7.1

8/2 4.7 3.8 3.6 3.1 3.4 3.0 2.1 2.8 5.6 3.2 5.0 2.7 8.0 3.7 10.8 6.7 9

8/9 8.7 10.0 7.5 6.7 6.2 2.0 8.1 5.5 17.9 4.6 13.0 5.8 20.0 2.5 13.1 4.2 1 ~ C 8/16 - - - - ul - - - - - - - - - - - -

8/23 - - - - 7.5 6.9 8.9 6.6 10.4 5.7 7.5 5.4 60.4 3.0 12.5 6.8

8/30 17.1 16.7 10.8 6.5 6.9 4.6 21.1 13.5 22.5 2.9 11.4 2.5 6.4 2.9 - 4.4

~ x 6.2 6.3 5.7 4.4 4.4 4.2 6.4 5.7 8.0 3.8 7.0 3.8 v

8.6 3.0 10.7 5.4 I

v Average exc lus ive of high value observed on 8/23.

I

I

Table 3. Correlation coefficents equal to or greater than + 0.80 or - 0.70, post Agnes Study, Patuxent River Estuary, 28 June to 30 August 1972.

Station Factors Correlation Coefficent d.f. P.

Nottingham Surf ace

Bottom

POSITIVE NO2 X TDN 0.87 NO3' X TDN 0.97 NO X TDN 0.87 TD& x DIP 0.95 TDN X TDP -b 0.87 DIP X TDP 0.90 TCL X ACL 0.996

NO3 X PC NO3 X TCL NO X ACL Ng3 X TCL l N i f X ACL TD# x PN TDN x PC TDN X TCL TDN X ACL TDN X SAL TDP X PC TDP X ACL TP X SAL

NEGATIVE -0.86 -0.86 -0.82 -0.85 -0.82 - .75 - .83 - .81 - .76 - .77 - .91 - .74 - .78

POSITIVE PE: X TCL .92 PN X ACL .92 TCL X ACL .99

NEGATIVE (NONE )

Lower Marlboro Surface POSITIVE

TCL X ACL 0.99

Bottom

Trueman Pt. Surf ace

NEGATIVE (NONE )

POSITIVE PC X SES .95

TCL X ACL .99

NEGATIVE (NONE )

POSTIVE TCL X ACL .99

NEGATIVE (NONE )

Tal - St, -

Station Factors Correlation Coefficent d.f P.

Bottom POSITIVE

PN X PC .84 PN X SES .83 TCL X ACL 1.00

NEGATIVE (NONE )

Benedict Bridge Surface POSITIVE

NO2 x NO3 .99 ~ 0 2 x TDN .88 NO3 x TDN .88 No3 x DIP .82 TCL x ACL .99

NEGATIVE NO x SAL -. 78 NO: x TCL -. 74 NO3 x ACL -. 76 NO x SAL -. 76 TDA x PC -. 71 TDN x SAL -.78 DIP x SAL -.70

Sheridan Pt. Surface

Queen Tree Surface

Bottom

Table 3. Continued.

1

POSITIVE TCL X ACL 1.00

NEGATIVE PC X SES -.71

Sheridan Pt. Surface POSITIVE

.96

.96

C2 7

PN X TCL PN X ACL TCL X ACL

NEGATIVE (NONE)

POSITIVE TCL X ACL 0.96

NEGATIVE e (NONE)

POSITIVE NO X TDN .85 T D ~ X sAL .84 TCL X ACL .99

NEGATIVE (NONE)

POSITIVE TCL X ACL .97

NEGATIVE (NONE )

Table 3. Continued.

Location Factors Correlation Coefficent d.f. P.

Broome Is. Surf ace POSITIVE

I

Bottom

PN X PC PN X TCL PN X ACL PN X SES PC X TCL .90 PC X ACL .89 PC X SES .89 TCL X ACL -B 1.00

PN X PC PN X SES PC X SES TCL X ACL

Sandy Pt. Surf ace

NOj X NH3 NO3 X TDN NH3 X TDN PN X TP PN X PC PN X TCL PN X ACL TP X TCL TP X ACL TCL X ACL

NO3 X TDP NO X SAL T D ~ x SAL DON X TP

Bottom PN X PC PN X TCL PN X ACL PC X TCL PC X ACL TCL X ACL

NEGATIVE (NONE)

POSITIVE .80 .82 .95 .87

NEGATIVE (NONE )

POSITIVE .82 .94 .85 .91 .84 .87 .86 .93 .94 1.00

NEGATIVE -. 73 -.70 -. 74 -. 78

POSITIVE .94 .86 .87 .94 -95

1,oo

NEGATIVE (NONE )

~ -

River Post-Agnes Study, summe; 1972.

STATIONS Nottingham Benedict Br. Queen Tree Sandy Pt.

C :N :P C:N:P C:N :P C:N:P Date

28 June 39:6:1 - 99:23:1 80:12:1

7 July - - - -

26 July 42:8:1 48:7:1 49:lO:l 78:11:1

16 Aug. 68:8:1 118:9:1 49:ll:l 129:21:1

23 Aug. - 107 :10 : 1 160:20:1 108:13:1

30 Aug. 69:37:1 218:ll:l 132:12:1 434:21:1

T a b l e 6. F l w o f materials t o t h e h e a d o f t h e P a t u x e n t R i v e r E s t u a r y , Post-Agnes S t u d y , summer 1972.

28 J u n e 42.6 33 1 . 4 1 .4 59.6 0.257 10 .9 73.8 44.0 2 .87

5 J u l y 2 1 . 1 54 1.1 2.0 42.2 0.257 5 .4 84.6 25.0 2 .38

1 2 J u l y 1 6 . 8 32 0.5 1 .4 23.5 0.355 6 .0 81.2 1 9 . 1 2.62

1 9 J u l y 1 8 . 1 32

26 J u l y 7 .9 48 0.4 2.5 19 .8 0.548 4 .3 5 6 . 3 6.2 2 .18

b

4.4 24

'estimates b a s e d o n f l o w and v a l u e s p r e c e d i n g a n d f o l l o w i n g m i s s i n g d a t a . %ased 04 DIP.

- Q ~ is a n e s t i m a t e o f t o t a l f r e s h w a t e r d i s c h a r g e t o t h e head o f t h e e s t u a r y .

Appendix. Patuxent River Post-Agnes Data Summary, summer of 1 9 7 2 .

Seston (mg liter-') -

DATE Station

Sandy Pt. T B

Broome Is. T B

Queen Tree T B

Sheridan Pt. T B

C) Benedict Br. T W B

Trueman Pt. T 8 7 6 7 4 8 5 0 6 4 3 5 32 - 4 8 3 2

I B 8 0 1 2 0 4 8 4 0 3 5 6 4 6 4 - 4 8 4 8

L. Marlboro T 40 47 3 2 32 4 8 56 2 4 - - 2 4 B 6 0 1 7 0 4 0 4 0 4 0 ;36 2 4 - - 4 8

Nottingham T 2 7 54 2 4 32 4 8 7 2 3 2 - - 2 4 B 4 0 5 4 4 0 3 2 4 8 1 6 8 4 8 - - 2 4

Active Chlorophyll a continued on next page.

A c t i v e C h l o r o p h y l l a (mg m-3)

S t a t i o n 6/2 8 7/5 7/12 7/19 7/2 6 812 8/ 9 8/16 8 /23 8/30

Sandy P t . T 46 .0 1 3 . 2 33 .5 35.9 31.2 1 9 . 2 38.3 9 . 3 44.9 54 .5 Ei 2 . 0 5 . 7 3 .6 38.3 1 8 . 0 2 6 . 3 1 0 . 2 5 5 . 1 9 .9 6 . 3

Broome Is. T 44 .0 1 8 . 0 1 8 . 0 22 .4 9 . 8 31 .2 74 .2 1 6 . 2 127 .2 1 8 . 0 B 1 . 5 2 . 2 5.6 7 . 3 6 .9 7 . 2 5 . 7 4.6 4 .3 4 . 5

B e n e d i c t Br . T 3.0 8 . 7 1 5 . 6 29 .9 35 .3 1 3 . 2 49.4 1 9 . 2 29.2 38.3 B 2.0 6 . 8 9 . 6 39 .0 4 9 . 1 1 0 . 8 40.4 27.5 1 5 . 5 1 8 . 0

n Trueman P t . W

T 6 . 0 8 . 6 1 6 . 3 29.9 28.7 1 0 . 8 46.4 31 .1 23.9 18 .9 w B 4 .0 8 . 7 1 4 . 9 28 .7 38.3 8 . 2 34.4 28.7 27 .5 19 .2

T o t a l C h l o r o p h y l l 5 (mg m-=)

Sandy P t T 5 2 . 7 17 .6 3 8 . 5 4 0 . 3 36.6 23.4 44.6 11 .9 54.4 66.6 B 3 .5 8 .7 5 . 7 43.9 22.0 31.5 1 3 . 0 64.4 1 3 . 2 8 . 0

Broome Is. T 51 .3 21 .2 21.2 28.2 1 4 . 2 38.8 83.4 19 .0 1 4 9 . 7 22.0 B 2 . 5 4.9 8 .9 11 .9 1 1 . 0 7.8 11 .4 6.0 5 .6 6.6

Queen T r e e T 29 .5 25.6 30.8 43.2 1 4 . 7 19 .8 64.4 23.4 1 8 . 7 39.9

B 2 .5 11 .7 7 . 0 1 1 . 4 19 .0 1 3 . 2 23.4 5 . 2

T o t a l C h l o r o p h y l l 5 c o n t i n u e d o n n e x t p a g e

~

~~ - -- - ~- . -

T o t a l C h l o r o p h y l l a c o n t i n u e d

S t a t i o n 8/23 8/30

S h e r i d a n Pt. T 11 .0 14 .4 20.5 36.6 16.8 24.2 71.7 34.4 3 6 . 1 46.4

Bened ick Br. T 4.0 11.6 20.5 38.5 44.6 17.6 58 -6 23 .4 35.2 41.2 B 3.5 10.4 14.6 48.5 60.0 17.6 51.2 32.9 19 .5 19.3

Trueman Pt . T 9.0 11.2 22.5 38.5 37.3 14 .6 57.6 42.5 30.7 24.4 B 6.0 12 .8 20.7 36.6 46.8 13 .5 45.8 36.6 35.1 24.9

L. Mar lbo ro

No t t i ngham

-1 P a r t i c u l a t e Carbon (mg l i ter )

3.0 14.6

Broome Is.

Queen T r e e

S h e r i d a n P t .

B e n e d i c t Br.

Trueman P t .

P a r t i c u l a t e Carbon c o n t i n u e d on n e x t page.

Particulate Carbon continued

8/23 8/30

L. Marlboro

Nottingham

Particulate Nitrogen (dl9 liter

0.441 0.823 0.250 0.162

Broome Is, 1.584 0.316 0.346 0.166

Queen Tree 0.231 0.356 0.144 0.100

Sheridan Pt. 0.352 0.465 0.202 0.164

Benedict Br. 0.342 0.458 0.258 0.295

Trueman Pt. 0.170 0.511 0.385 0.317

L. Marlboro

Nottingham

I

L

O N 0 W N N . . . o r l m

r l m m -ell? O O N

r l m m o m * . . . O O N

N m '3 m o m . . . O d *

V ) mm FJII w m u , N m m O W * . . . . . . O O d d r l m

'14: r l r l w

mu, m m

* I rl

dm*

. * * o0

a - m w m w . . . rl Nu,

*3 NO2 NO3 DON TDN

NO3 DON TDN

A m n i a (m3), n i t r i t e (NO2), n i t r a t e (NO3), d i s s o l v e d o r g a n i c n i t r o g e n (DON) and t o t a l d i s s o l v e d nitrogen(^^^) a t the s u r f a c e (pg a t l i ter -1) .

Sandy P t .

Queen T r e e

Bened i t Br .

Nottingham

16.0 13.9 6.9 9.3 - 3.1 - 0.6 - 1.4 2.0 2.3 2.3 - 2.1 1.9 1.0 -

41.7 45.0 49.7 50.8 - 27.6 19.2 14.4 - 13.9 23.8 22.3 29.0 - 31.3 - 22.6 - 73.0 84.9 81.2 91.4 - 64.1 - 38.6 -

P A T U X E N T R I V E R

Fig. 1. Map of the Patuxent River estuary showing station locations.

80 ' Nottlnghom

0 surface - I

r 1 bottom

4 0 -

0 . I

8 0 Trueman Point

- - 'L 4 0 - .- - 6 0

I

Benedict Bridge

0 I-

v, u 0

Sherldon Point

1 Queen Tree Landing 1

Broome Island - 4 0 -

r 0 . -,

4 0 1 I Sandy Point 1

- 28 1 , 5 12 19 9 16 23 30

June July August

Fig. 2. Surf ace and bottom s e s t o n c o n c e n t r a t i o n s (ng l i t e r - l ) observed i n t h e Pa tuxen t River e s t u a r y dur ing t h e Post-Agnes Study, summer 1972.

F i g . 3a. S u r f a c e c o n c e n t r a t i o n o f a c t i v e c h l o r o p h y l l 5 (mg mb3) obse rved i n t h e P a t u x e n t R ive r e s t u a r y d u r i n g t h e Post-Agnes Study,summer 1972.

Broome 1%

Sandy Pt.

July I August

F i g . 3b. Bottom c o n c e n t r a t i o n of a c t i v e c h l o r o p h y l l 5 (mg m-3) obse rved i n t h e P a t u x e n t R ive r e s t u a r y d u r i n g t h e Post-Agnes S tudy , summer, 1972.

C40

- m

6 2 , U L . U . 4 U S -

O % m . 4 0 : O:zK UL. L . 4 . r l o u m c m a :

Q > I ? m m.4 0 4 U > m U m m 4 rl O U W U 3 m c u m u m m m

.4 .4 X u ua 3 m m L. U a I E m a m L . m a c e i 3 4

4 0.h w -.4 o - m w I? - c 0 -a 0 m L.

4 H - 4 C W I a u u - u - m m u c m

pl ~ c m . 4 ~ - . d m m r l g p g 4

U L i U O U m U 4 U C a m 3 V)

5"; S - u m .a:

.rl -4 C O R ~ R ~ ~ C C U P - ' 0

.rl tn-rl m U u m o a u h p # z m a u m c m L I c > m 0 o r l tJ - w U 0 0 h

m u a m m m u 9 u C .4 .4 U m ~ a ~ m a